Pneumatic rubber tires are conventionally built from tire components, such as the tread, sidewalls, belts, beads, innerliners, etc. having specific characteristics chosen to affect the performance and life of the tire. The tire components are generally comprised of different elastomeric compositions that provide the specific desired characteristics necessary for the tire. Some tire components, for example, tire sidewall layers, apex, treadbase, Extended Mobility Tire insert (“EMT insert”), wedge, gum strip, and wire coat, may be subjected to considerable flexing, scuffing, and/or atmospheric aging. These tire components necessitate elastomeric compositions having increased stiffness, and improved resistance to tearing, flex fatigue, and ozone.
Fatigue cracking of tire components, when it occurs, is usually due to continual flexing of the tire component as the tire is run under load at service conditions. Fatigue cracking may be exacerbated by atmospheric aging.
To prevent fatigue cracking and increase the stiffness of tire components that require greater stiffness, such as apex, EMT inserts, treadbase, etc., the elastomeric compositions that make up the tire components have conventionally been reinforced by incorporating large amounts of carbon black and/or silica into the compound and/or by increasing the state of cure. Unfortunately, these techniques offer only diminishing returns and can actually result in decreased resistance to flex fatigue and tear strength.
Of further concern, tire components exposed to the atmosphere, such as the visible outer layers of an elastomeric tire sidewall, may age somewhat prematurely as a result of, for example, weather aging. For example, weathering may prematurely age exposed tire components as a result of exposure to ultraviolet light, ozone, and/or high humidity. Antidegradants are conventionally mixed with the sidewall elastomer to counteract or retard such effects.
Tires having improved stiffness and resistance to tearing, flex fatigue, and ozone, have met with great market success. Then, it would be desirable to provide a tire comprised of components of longer lived elastomeric compositions and/or improved performance.
One technique to improve stiffness and resistance to tearing, flex fatigue, and ozone, is to incorporate different fillers into the elastomeric composition. One class of potential fillers are polyamides. Polyamides may be added to the elastomeric composition as particles such as fibers, spheres, or pellets. In order to achieve the full benefit of the polyamides, the particles must be melted to obtain adequate dispersal in the elastomeric composition and the polyamide must bond with the elastomeric component of the elastomeric composition.
Polyamides that have previously been incorporated in elastomeric compositions have had relatively high melting temperatures, generally in excess of 200° C. The high temperatures required to melt these polyamides can damage other components of the elastomeric composition. Thus, in order to prevent heat damage to the other elastomer components, a separate polyamide melting step is added to the elastomer compounding process, thereby decreasing efficiency and increasing cost.
Polyamide bonding to the elastomeric component of elastomeric composition using standard techniques may be sufficient for some applications, however, it may be desirable to improve the bonding for other applications. Standard curing techniques include the use of sulfur containing curing agents, heat, and pressure.